My students had to identify the main verbs in a paragraph and mistakenly marked a few infinitives like the following:

Chop the carrots into small pieces to make them cook faster.

So I explained that the infinitive bolded above is working more like an adverb. Compare the above sentence to the following:

Chop the carrots in small pieces quickly/efficiently/whimsically.

Infinitive verb phrases like these provide a reason for the main verb (chop), and thus, it is not the main verb of the sentence.

Person A: "Why did you chop the carrots into small pieces?"Person B: "To make them cook faster."

I then wrote the following sentence on the board as an example:

She ate the soup to make him happy.

This example looks a bit contrived, but it really happened. I made some soup last weekend that turned out pretty bad, so I couldn't help but tell my class this story about my wife's polite endurance and my two-year-old son's brutal honesty:

"UGH! OH YUCK!" "Charlie! We don't say 'yuck' with food. It's very rude." "Daddy, this soup is not very good." (Honestly, it was real bad)

Me: "See, this part, 'to make him happy,' is the reason. You could ask, 'Why did she eat the soup?' and the answer would be, 'to make him happy.'"

Student: "Eat it?"

Other Student: "No, drink it."

Student: "Drink the soup!"

Me: "I'm sorry, what?"

Other student: "It should be drink!"

Me: "Oh, okay, I see. Yes, in many languages you drink soup. I know that in Japanese, Chinese, Korean, and Arabic, you drink soup, but in English, you eat it."

Students: "Whaaaat?! Why?!"

Luckily, I found out from a German-speaking colleague that Germans eat their soup as well, so I knew there was some safety in numbers and I was able to cite that as another example:

Me: "I don't know, but in English and in German, most of our soups have pieces in it that you have to chew. Anyway, you can say 'drink soup,' and people will get what you mean, but it will just sound weird."

Student: "I think you should change your way." (if more languages say drink, then English should do that, too).

I'm not so familiar with Middle-Eastern soups, but I know the soups I encountered in Korea and Japan were mostly liquid, and they were quite drinkable. Most American soups, on the other hand, are not. Of course this is all anecdotal and based on my own limited culinary knowledge, but I think the soups of European descent (if there were such a thing--we'll need genetic testing to be sure) seem to be chunkier in nature. Even drinkable soups like tomato soup are often accompanied with a grilled cheese sandwich, an instantiation of the Soup and Sandwich Phenomenon (on a side note, while I was conducting grilled cheese research, I discovered "the cheese dream." Thank you, Wikipedia for documenting this gem of an Americanism).

I don't know why, but these kinds of interactions intrigue me every time. The shock and surprise in my students' voices when they hear something strange about English--their reaction, it's always new, always sudden, that I feel like I get to learn it all again along with them. It never gets old.

How about you? Are there any things you teach that always seem to surprise your students? Do you get a kick out of seeing them discovering the weirdness of English?